Volume control



Patented June 9, 1931 TJNITED STATES LAWREl-VCE T. PHELAN, OF PHILADELPHIA, PENNSYLVANIA VOLUME CONTROL Application filed April 11,

My invention relates to a method of, and apparatus for controlling the amplitude of signals reproduced by a telephonic device, and particularly by a loud speaker associated with radio receiving apparatus having a plurality of amplifier stages, and circuits tunable to receive music, speech, and the like, generically termed signals transmitted from selected stations.

When the modern radio receiver is adjusted for great sensitivity and the tuning devices of the selective circuits adjusted in efi'ort to receive from weak or distant transmitting stations, signals from powerful or local stations are reproduced at excessively high volume and often, due to overloading either of the loud speaker, or of the tubes of the receiving set, or both, with distressingly marked distortion.

In accordance with my invention, when the apparatus is tuned to the frequency of disturbing station, its sensitivity is depressed to a point at which the signals are reproduced with good quality and at suitable volume, and as the apparatus is tuned to another of different frequency, the sensitivity thereof is restored to permit reception of signals from more remote or weaker stations at normal volume.

Further in accordance with my invention, there is provided an impedance adjustable by an operator, independently of tuning, to effect control of volume, and the change in amplitude of a signal effected by the impedance controlled by the tuning operation is determined by the setting of the first, or manually operable impedance; more specifically and preferably, the impedances are difi'erentially and simultaneously adjustable, as by a common operating member, the change in sensitivity being great when the set is adjusted to respond to more feeble energies, and small when the set is adjusted to a less sensitive condition.

My invention further resides in the methods, and the electrical and mechanical features of operation and arrangement herein described and claimed.

For an understanding of my invention and for illustration of some of the forms it may 1929. Serial No. 354,240.

take, reference is to be had to the accompanying drawings, in which:

Fig. 1 discloses schematically the circuit arrangement of a complete radio receiving apparatus embodying my invention.

F 2 illustrates schematically radio receiving apparatus utilizing a modified form of my invention.

Fig. 3 shows diagrammatically a further modification of my invention.

Fig. fl is a side elevational view, with parts in section, of a mode of mechanical connection between a tuning device and a switch controlling the circuit position of a volumelimiting impedance.

Fig. 5 is a front elevational view of parts 1 shown in Fig. 4. 4

Fig. 6 is a fragmentary view, on enlarged scale of parts shown in Fig. 4:.

Referring to Fig. l, the conductors 1 and 2, operatively related to the input element T of thethermionic tube V, are connected respectively, to the antenna 3 and to earth E, or equivalent. It will be understood, however, that they may be connected to a loop antenna, or to the conductors of a wired wireless system. Energy absorbed by the antenna system flows through the primary P of the transformer T effecting change in voltage of the control grid 9 of tube V in Whose anode or output circuit is included the primary P1 of transformer T1 whose secondary S1 is connected to the input electrodes 9 and f of thermionic tube V1. If desired and as shown, the energy may be further amplified at radio frequency by amplifier tube V2 in whose input circuit is included the secondary S2 of transformer T2 whose primary P2 is in the anode circuit of tube V1.

Between the detector tube V3 and amplifier V2 may be interposed additional radiofrequency amplifier stages but for simplicity of explanation, the input element of the de-' tector, specifically the transformer T3 is shown as having its primary P3 in the anode circuit of tube V2. The usual grid condenser C and grid leak resistance R co-operate with tube V3 to demodulate or rectify the amplified energy, although if desired, a plate current rectification circuit may be utilized. 3

The audio-frequency variations of current in the anode circuit of the detector tube are amlified by tube V4 in whose input circuit is included the coupling element or transformer T4 having its primary P4 in the plate or anode circuit of the detector. A by-pass condenser C1 of low impedance to currents of radio frequency is connected between the lower end of rimary P4 and filament or cathode f of tu V3. The anode a of the audio amplifier tube V4 is connected to a suitable source of direct current, generically represented by the batter B, throu h an inductive reactance L of igh impe ance to currents of audio-frequency. A loud speaker LS is connected in series with a condenser C2 of low impedance to currents to audio-frequency between the anode a and cathode f of tube V4.

The resistances R1 in the cathode or'filament circuits of the amplifier tubes V, V1, V2 and V4 are utilized to determine the cathode temperature and to bias the grids g to a suitable negative value. Particularly when the source of current for energizing or heatingthe cathodes is a battery A, as indi cated, thresistance R3 preferably in circuit with the cathode or cathodes of one or more radio frequency amplifier tubes, may be varied to control the volume of signals re roduced by the loud speaker LS. Preferab y, and particularly whenthe cathodes are heated by current derived from a source of alternating current adjustment of contact 4- alon resistance R4 in shunt to the primary P o the input transformer T efiects control of volume without the introduction of hum, or distortion.

To select a desired signal from other si nals, the apparatus is provided with tunab e circuits hav ng devices capable of adjustment to efl'ect resonance at the frequency of the desired signal. To that end, one and preferably more of the amplifier stages are tunable b condensers,as variable condensers K1, and 2. The input circuit of the first tube V is not tunable to permit simultaneous adjustment, as b a sin le control, of condensers K1, K2 an also 0% condenser K3 tuning the detector input circuit.

Durin operation of the set, as thus far describe when the volume controlling resistances R3 and/or R4 are adjusted for great sensitivity, for example, when the contact 4 is at or near the lower end of resistance R4, as the rotors of the condensers K1, K2, and K3 are moved in an effort to pick up .signals from distant or weak stations, the signals from powerful or local stations are reproduced b the loud s eaker at excessively high level of volume; irther due to overloading of the tubes, transformer T4, loud eaker, or any one or more of them, the s1 nal is badly distorted.

o avoidthis disturbing effect, the volume rendered effective when, and preferably 0 y when, the circuits are resonant at the frequency of the disturbingly powerful signal.

In the specific arrangement of Fi 1, one or more contacts or switch arms 5, o a number dependent upon the number of interfering stations, are actuated to engage a fixed contact 6 when a tuning condenser with which it is associated for simultaneous movement, is in a position effecting resonance of a selective circuit of the receiver at the frequency of transmission of a local station, for example. This automatic limiting of volume may be prevented when desired by opening the switch a in series with the resistance R5 and switch 5, 6 in the path between conductor 1 and earth E. Control of volume of all signals, including those of local stations, is then completely at the will of the operator, and is inde endent of tuning adjustments.

As an ternative, the resistance R4 or equivalent may be connected between contact 6 and earth E, insteadof in the position shown the terminals of primary P being directly connected to antenna 3 and ground E. In

this arrangement, the setting of rheostats R5 and R4 determines normal sensitivity and of R5 the depressed sensitivity efi'ected when a contact 5 engages the co-operating contact 6 in response to movement of the condensers to a position efl'ecting resonance of the circuits at the frequency of transmission from stations whose signals would otherwise be reproduced with undue volume.

11 the modification of my invention shown in Fig. 2, as the position of contact 4 is varied along resistance R4 by an operator to determine the sensitivity of the receiver, there is simultaneousl efi'ected change in position of a contact 7 a ong resistance R5 so that the efiectiveness of resistance R5 when included in circuit, or change in sensitivity effected by its inclusion, is dependent upon the degree of sensitivity selected by the operator. For example, when the contact 4 is at or near the lower end of resistance R4 to, effect great sensitivity, the condition under which local signals will be greatly disturbing, the contact 7 1s adjacent the upper end of resistance R5 for substantially maximum shunting efi'ect and decrease of sensitivity when the control circuit including it is completed by engagement between contact 6 and any one of contacts 5 operated from the tuning condenser actuating means. On the other hand when the contact 4 is adjacent the upper end of resistance 4 for the reception, at comfortable volume, of moderately strong signals for example, the contact 7 is nearer the lower end of resistance R5 to reduce the shunting effect, and depression-of sensitivity produced thereby. The lengths of resistances R4 and R5 or relative movement of contacts 4 and 7 may be proportioned so that when contact4 is practically at its extreme upper position for the reception, at suitable volume, of local stations, the contact 7 is out of engagement with resistance R5.

Obviously in either modification, the impedance R5 may be a resistance, an inductance, or a capacity if suitable values are selected. Further the change in impedance efi'ected by the act of tuning may be of elements already included in the receiver. For example, contacts 5 may be designed to open a shunt circuit about a resistance included in series with resistance R3 in conductor 1 or 2, or in series in the anode circuit of one or more of the tubes. In Fig. 3, radio frequency energy is diverted from the primary of transformer Tn when the contact 6 is engaged by a contact 5 to complete an alternating current path including resistance R5 and a condenser C3 of low impedance to radio frequency currents.

When one or more of the electrodes are energized from an alternating power source, rectified or not, it is advisable to effect control of volume without change of potential or of energy therefrom to the electrodes. Any of the arrangements shown are suitable for use in systems in which the cathodes, the anodes, and the grids, or any one or more of them, may be supplied from an ultimate source of alternating current. When screengrid tubes are used, the volume may be conveniently controlled by changing the positive potential of the screen grid, reducing it to lower volume and vice versa.

As an illustration of one of the many possible mechanical arrangements of operatively relating the tuning devices and a volume controlling element, reference is made to Figs. 4 and 5. The condenser K is provided with a rotor shaft 7 of sufficient length to project beyond and exteriorly of the front panel or wall 8 of a cabinet or housing for the receiving apparatus. Movement of the dial 9 connected to shaft 7 by varying the position of the rotor plates with respect to stator plates 11 tunes a circuit associated therewith through a band of wavelengths. A band or the like passing over the drum 12 secured to shaft 7 connects for simultaneous movement the rotors of other tuning condensers. One end of the metal shaft 7 is supported by a bearing 13 and to the other end is secured a collar 14 to which is fastened the two flexible, metal discs 15, 15 having crimped or corrugated rims 16. Needle-like contact pins 5 are inserted between the discs in positions determined as hereinafter described and clamped by tightening of the bolts 17 to draw plates 15 more intimately together.

Adjacent the periphery ofthe discs 15 is positioned a member 18 of any suitable insulating material and having a small reservoir of restricted bore containing mercury,

the meniscus of which projects into or intercepts the path of movement of contacts 5 and forms the fixed contact 6, previously described. The element 18 may be secured to a standard 19 engaging the collar 14 to assist in the support of shaft 7, by screw 20 threaded therein and preferably in electrical contact with the mercury to provide a terminal to which a conductor 20 may be connected.

To set the apparatus to effect the operation previously described, the dial or knob 9 is turned to position at which a local or powerful station is received. A contact 5 is then inserted between the discs and adjusted so that its tip just engagesthe mercury contact 6 completing a circuit through the volume con trol resistance R5. The bolts are tightened slightly to hold the contact 5 firmly in its adjusted position from which it is not disturbed unless the local station changes its wavelength or the location or constants of the receiver is changed. For each disturbing station there is a corresponding contact 5 which in the arrangement shown'is diametrically opposite the dial setting for the station.

After all contact pins 5 are in place, the screws 17 are further tightened to preclude their loss of adjustment. Thereafter the set may be operated with any desired sensitivity including the maximum which is extremely high when screen-grid tubes are used, particularly in the radio-frequency amplifier stages without the discomfort and disturbance hithertofore experienced when during adjustment of the tuning devices, the circuits associated therewith became resonant at the frequency of a nearby transmitter.

It is apparent that the nature, circuit position, and mode of connection to the moving element of a tuning device, of the volume control impedance R5 may vary from the specific disclosure without departure from the spirit and substance of my invention.

What I claim is:

1. In the operation of radio receiving apparatus having one or more circuits tunable by adjustment of the movable elements of tuning devices associated therewith, the method which comprises moving said elements continuously to change the resonant frequency of said circuits in search of signals from a desired station, and utilizing the movement temporarily to depress the sensitivity of the apparatus as the resonant frequency of the circuits passes through transmission frequency of nearby or powerful stations.

2. In the operation of radio receiving apparatus having means to. adjust sensitivity and one or more circuits tunable by adjustment of the movable elements of tuning devices, the method which comprises adjusting said means to effect desired degree of sensitivity, moving said elements continuously to change the resonant frequency of said circuits in search of signals from a desired station, and utilizing the movement temporarily to depress the sensitivity as the resonant frequency of the circuits passes through the transmission frequency of nearby or powerful stations, toan extent determined by the degree of sensitivity effected by said adjustment.

8. In the operation of radio receiving apgaratus having one or more circuits tunable y adjustment of the movable elements of tuning devices associated therewith, and impedance controlling the amplitude of reproduced signals, the method which comprises moving said elements continuously to change the resonant fr uency of said circuits in search of signals mm a desired station, and utilizing the movement to effect temporary change in the effective magnitude of said impedance as the resonant frequency of the circuits passes through the frequency of transmission from nearby or powerful stations, in a sense reducing the amplitude of signals therefrom. 4. In the operation of radio receiving apparatus having one or more circuits tunable by adjustment of the movable elements of tuning devices associated therewith, and impedances controlling the amplitude of reproduced signals, the method which comprises adjusting the magnitude of one of said impedances to effect desired'normal sensitivity, simultaneously varying the magnitude of other impedance without efl'ect upon normal sensitivity, moving the elements of said de; vices to select a desired station, and utilizing the movement to render said other impedance effective when the circuits are resonant at the frequency of transmission from nearby or powerful stations to depress the sensitivity in a'sense to depress sensitivity when said dial is at a setting corresponding to the frequency of transmission from a powerful station.

7. Radio receiving apparatus comprising absorption structure, .an input transformer having a primary winding in circuit with said structure, cascaded thermionic tubes, tunable circuits associated therewith including tuning devices having adjustable elements, a sound reproducing device, a radio frequency path in shunt to said primary winding, and means to reduce the impedance of said path to prevent excessive volume of signals from local stations operated by said adjustable elements as they pass through positions corresponding to the transmission frequencies of said stations.

LAWRENCE T. PHELAN.

to an extent determined by the first adjustment.

5. Radio receiving apparatus comprising cascaded thermionic tubes, tunable circuits including tuning devices having adjustable elements, a sound reproducing device, an im pedance adjustable to effect desired normal degree of sensitivity, a second impedance adjustable simultaneously with and in opposite sense to said first impedance, normally having no effect upon sensitivity, and means operable in unison with said adjustable elements throughout their range of movement varymg the effective magnitude of said impedance 

